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扬子板块西缘的四川泸定桥头基性杂岩体主要由辉长岩组成。辉长岩中锆石的结晶年龄为 85 3± 4 2Ma ,表明它形成于新元古代早期。该岩体的主量元素显示钙碱性分异趋势 ;微量元素呈现典型的岛弧环境地球化学特征 ,即相对富集大离子不相容元素 (Sr ,Rb ,Ba) ,亏损高场强元素 (Nb ,Ta ,P ,Ti)和LREE轻微富集 ((La/Yb) N=2 .0 7～ 6 .77) ,配分型式略呈右倾型 ;εNd,ISr和δ18O值分别为 2 .5～ 3.1,0 .70 2 6 2～ 0 .70 5 12和 1.94‰～ 6 .32‰ ;在微量元素构造环境判别图上 ,它们都投影于岛弧拉斑玄武岩区域内。上述特征表明 ,泸定桥头杂岩体可能是在一个相对原始的岛弧环境中形成的 ,岩浆源区已受到俯冲组分影响而产生不同程度富集。
The Sichuan Luding bridgehead complex complex in the western margin of Yangtze Plate is composed of gabbro. The grit age of gabbro is 85 3 ± 4 2Ma, indicating that it was formed in the early Neoproterozoic. The major elements of this rock mass show a tendency of calc-alkaline differentiation. Trace elements show the typical geochemical characteristics of island arc environment, that is, relative enrichment of large ion incompatible elements (Sr, Rb, Ba), loss of high field strength elements (Nb, Ta, P, Ti) and LREE were slightly enriched (La / Yb) N = 2.07-6.77, and the distribution patterns were slightly right-handed. The values of εNd, ISr and δ18O were 2.5 ~ 3.1,0 .70 2 6 2 ~ 0 .70 5 12 and 1.94 ‰ ~ 6 .32 ‰ respectively; all of them are projected on the island arc tholeiitic basalts on the discriminant map of tectonic environment of trace elements. The above characteristics show that the Luding Qiaotou complex may be formed in a relatively primitive island arc environment, and the magmatic source area has been affected by the subduction components and enriched to some extent.